Coated fiber product with adhered super absorbent particles

ABSTRACT

Discontinuous fibers are coated with a binder material with the binder material adhering the fibers to super absorbent particles. Fibers in the product are substantially unbonded except to the super absorbent particles. The binder may be present at an amount which is sufficient to substantially continuously coat the fibers. Plural coatings of various binder materials may be used. The binder material may be heat fusible or heat curable and the treated fibers mixed with other fibers for use in producing a wide variety of products.

This is a division of application Ser. No. 07/326,188, filed Mar. 20,1989, now U.S. Pat. No. 5,230,959.

BACKGROUND OF THE INVENTION

The present invention relates to discontinuous fibers with a bindermaterial to which super absorbent particulate materials are adhered. Thebinder may be of a heat fusible material which is applied as a liquid tofibers entrained in a gaseous medium. The particulate super absorbentmaterial is adhered to the fibers by the binder material as the bindermaterial dries and without heat fusing the binder to adhere theseparticles.

A number of techniques for applying binders to webs of fibers are known.For example, U.S. Pat. No. 4,600,462 of Watt describes a process inwhich an adhesive binder is sprayed onto one or both surfaces of an airlaid cellulose fiber web. Submersion of the web in the adhesive binderis another method disclosed in this patent of applying the binder.Individual binder coated fibers for mixing with other fibers are notproduced by this process. A hydrophile solution is also applied to theweb. As another example, U.S. Pat. Nos. 4,425,126 and 4,129,132 ofButterworth, et al. describe a fiberous material formed by combiningthermoplastic fibers and wood pulp, heat fusing the combined fibers, andthereafter depositing a binder on the heat fused web. Because the fibersare heat fused prior to adding the binder, individual binder coatedfibers for mixing with other fibers are not produced by this process.

U.S. Pat. No. 4,584,357 of Harding discloses a latex treated cationiccellulose product and method for its manufacture. In the Hardingapproach, cationized cellulose is treated in an aqueous suspension withan anionic polymer emulsion of from 0.1 to 30 percent on a dry weightbasis. The patent mentions that the resulting resin treated products canbe prepared in sheet form, as loose fibers or in another form. Theapproach of the Harding patent is limited to cationic fibers. Also, thefiber coating applied as described in the Harding patent had a tendencyto flake off or separate from the fibers. Moreover, because the Hardingapproach uses a wet process, the lumen of the cellulose fibers ispenetrated by the polymer emulsion. Since the binder on the surface ofthe fibers contributes principally to the desired characteristics of thefiber, any polymer that penetrates the lumen of the fiber adds little tothese desired characteristics.

U.S. Pat. No. 4,469,746 of Weisman et al. discloses fiberous webscomprised of fibers coated with a continuous film of silica. The fibersare understood to be dispersed in a charged silica aquasol to accomplishthe coating. Because silica is an inorganic material, the silica doesnot contribute to subsequent bonding of fibers. In addition, becauseWeisman et al. discloses a wet process, the silica will tend topenetrate the lumen of cellulose fibers in the event such fibers arebeing treated in accordance with this patent.

U.S. patent application Ser. No. 067,669, filed Jun. 26th, 1987, andentitled "Treated Wood Fiber Having Hydrophobic and OleophilicProperties", by Jewell et al., mentions an approach of treatingfiberized wood with surfactant material to penetrate the surface of thewood fibers. In this approach, fiberized wood at the outlet of a firstfiberizing machine passes through an orifice into a blow line. At theoutlet of the fiberizing machine, liquid surfactant is injected into theline. At the point of addition of the surfactant, the fiber is still wetas it has been carried by steam through the fiberizing machine.Surfactants are not suitable for use in subsequent bonding of thefibers. The Jewell et al. patent application also describes a process inwhich fibers are treated with a copolymer latex, such as a combinationof a paraffin wax emulsion and a styrene butadiene copolymer latex. Thepatent describes a suitable treating process as involving the blendingof the aqueous latex emulsion with wood fiber in a typical mechanicalwood fiber blender. This approach tends to produce fibers which arebound together by the latex.

U.S. Pat. No. 2,757,150 of Heritage mentions a fiber treatment approachin which fibers are carried by steam under pressure and in which athermoset resin is introduced into the fiber stream. Other materials(i.e. rosin and wax) are mentioned as being simultaneously introducedinto the fiber stream. The patent indicates that such materialspenetrate the surface of the fibers. This patent mentions theindividualization of these treated fibers. A relatively lowconcentration of the thermoset resin (i.e. two percent by weight phenolformaldehyde) is specifically described in this patent. At such lowconcentrations, the resin is in discontinuous random non-interconnectedareas (blobs or globules) on the fibers. These treated fibers aretypically used in hardboard. In current hardboard resin productsproduced using the approach of the Heritage patent and known to theinventors, a phenolic resin concentration of from a maximum of five tosix percent by weight is used. Even at these concentrations, the resinforms random non-interconnected globules on the fibers. As a result, theuncoated resin free areas of the fibers lack the capacity to bond incomparison to the areas of the fibers covered by the resin. In addition,the untreated surface areas of the fibers may lack desiredcharacteristics of the resin covered areas of the fibers. For example,these uncoated areas may cause the fibers to be more water absorbentthan if the entire fiber were coated.

U.S. Pat. No. 4,006,887 of Engels describes a process for treating woodfibers in which the fibers are supported as an annular loose fluidizedbed in a mixer which delivers glue by way of shaft mounted mixing rodsto the fibers. The patent mentions that radial air vortices areestablished with the mixer inlet and outlet funnels being connected toan air transport pipe. The patent describes the resulting product ashomogenous lump free uniformly coated wood fibers. The patent mentionsthat the coating of fibers is useful in the manufacture of wood fiberpanels. The glue used in the Engels patent and the percentage of theglue that is used is not discussed.

The background portion of the Engels patent describes GermanAuslegeschrift 1,048,013 as disclosing an impeller or agitator mixer forthe coating of wood chips with dusty components. Glue is described asbeing sprayed through nozzles into a mixing container. An air stream isdescribed as being blown axially through the mixing container in orderto reduce the residence time of dusty chip particles to reduce excessivecoating of such dusty particles. Also, German Offenlegunge 1,632,450 ismentioned by Engels as disclosing wood chips agitated in an air streamin a mixing tube in which glue spray nozzles are mounted.

Heretofore, synthetic bicomponent fibers have been formed by extrudingtwo materials in air in side-by-side strands which are connectedtogether along their length. Such bicomponent fibers have also beenformed with one material being extruded as a concentric sheathsurrounding the other material. These extruded strands are then choppedor broken into discontinuous fibers. Although synthetic bicomponentfibers provide good structural efficiency, they are very expensive incomparison to natural fibers, and, therefore, their use is limited.

U.S. Pat. No. 4,261,943 of McCorsley, III describes the extrusion offilaments and the application of a solution of a nonsolvent liquid tothe filaments. In this application process, the filaments are passedthrough a chamber having a nonsolvent vapor laden atmosphere, i.e. a fogof minute particles of nonsolvent. Spraying of the nonsolvent liquidonto the filaments is also mentioned. The approach of the McCorsley, IIIpatent is not understood to apply to discontinuous fibers.

U.S. Pat. No. 4,010,308 of Wiczer describes foamed porous coated fibers.Fibers, described as organic or inorganic fibers of any character, aredescribed as being coated with a foamable plastic material.Thermoplastic and thermosetting coatings are mentioned. In severalexamples, the coated fibers are made by passing continuous extrudedfilaments through a first bath of a ten percent polystyrene solution intoluene, evaporating the solvent, and passing the polystyrene coatedfiber through a second bath containing a blowing agent, such as liquidn-pentane. The treated filaments are then heated to foam the coating.Rolls are used to rub solid particles into the porous surface of thefoam coating. Fireproofing agents, lubricants such as graphite,pigments, and insecticides are among the examples of solid materialsmentioned as suitable for rubbing into the coating. In another example,short lengths of cotton linters are described as being wet with a tenpercent solution of a copolymer of polystyrene and acrylonitrile inabout equal proportions dissolved in benzene. The solvent is evaporatedin an air stream and the resulting coated cotton fiber is dipped inmixed pentanes. The product is then stirred in boiling water to causefoaming. Following foaming, the product is centrifugally dried and againdried in an air stream. The fiber is then mixed with a dry powder tofill the pores in the foamed coating with the powder. The placement ofthis fiber product in a container and heating the product to cause theadherence of the fiber surface contact points is also mentioned. TheWiczer patent appears to use a solution dipping approach as a means ofapplying the coating to the fibers.

U.S. Pat. No. 4,160,059 of Samejima describes a process in which anatural cellulose fiber (such as wood pulp fiber) is shredded andblended in air with a heat-fusible fiber. The blend is fed to adisintegrator to form supporting fibers to which an absorptive materialis added. Heated air is applied to the resulting web to heat the web toa temperature above the melting point of the heat fusible fiber to formbonds between the supporting fibers and absorptive material by heatfusion. Activated carbon black, Japanese acid clay, active alumina, anddiatomaceous earth are mentioned as representative absorptive materials.Other powders, including superabsorbents, are also mentioned as beingbonded in place in this manner. The background portion of thisparticular patent also mentions a process in which wood pulp isdisintegrated by a dry process, blended with active carbon black, andthe blend spread on a wire screen. A binding material such as latex,starch and the like can also be sprayed on both surfaces of the web.With this latter approach, the active surface of the absorptive materialis covered with a thin film of the binding material. Thus, under theSamejima approach, heat fusion is used to bind the particles to thefibers. As a result, a bound fiber web, as opposed to individualizedfibers, is formed with the particles heat fused to the fibers.

In U.S. Pat. No. 4,429,001 of Kolpin et al., melt-blown fibers areprepared by extruding liquid fiber-forming materials into ahigh-velocity gaseous stream. The stream of fibers is collected on ascreen disposed in the stream with the fibers being collected as anentangled coherent mass. Absorbent particles are introduced into thestream of fibers at the point where the fibers are solidifiedsufficiently that the fibers will form only a point contact with theparticles. The patent mentions that the particles can also be mixed withthe fibers under conditions that will produce an area of contact withthe particles. The introduction of other fibers besides melt-blownfibers into the resulting sheet product is also mentioned. The patentmentions that surfactants in powder form can be mixed with the sorbentparticles used in forming the web or surfactants in liquid form can besprayed onto the web after it is formed.

Finally, U.S. Pat. No. 4,392,908 of Dehnel describes a process forforming a thermoplastic adhesive resin on a surface of water solubleparticles. The coated particles in a dry state are heated and pressed tobond them to a dry substrate (i.e. cellulose fluff). Mixing of absorbentparticles with an aqueous latex, spraying resin onto the particles, andmixing the particles in a slurry are mentioned as approaches for coatingthe particles. Milling of the particles after coating with thermoplasticis mentioned as usually being necessary to produce free flowingparticles. Thus, the Dehnel patent illustrates another approach for heatfusing particles to fibers.

Although prior art approaches are known, a need exists for an improvedfiber product composed of fibers with a binder material and superabsorbent particles adhered to fibers by the binder material.

SUMMARY OF THE INVENTION

In accordance with the present invention, discontinuous fibers have abinder thereon in an amount which is sufficient to produce bicomponentfibers having a substantially continuous layer of the binder material ontheir surface. The coated fibers are stuck to super absorbent particlesby the binder, therefore, the particles are substantially prevented fromemigrating or escaping from the fibers. Also, as explained below, theparticles and fibers adhere without heat fusing any binder to accomplishthis result. A substantial majority of the resulting bicomponent fibersare unbonded to one another, although plural fibers are typicallyadhered to the same super absorbent particle. By using an organicpolymeric material as the liquid binder, and in particular a heatbondable liquid binder material, the fibers with the super absorbentparticles may be subsequently heated to fuse them together. The fibersmay also be combined with other nontreated fibers and heat fused toprovide a bonded web.

In accordance with the method, substantial amounts of binder materialmay be applied to the fibers with the process still producingindividualized coated fibers. However, it has been found that the firstbinder material must be applied in an amount of at least about sevenpercent of the combined dry weight of the binder material and fibers inorder to produce a substantially continuous binder coating on thefibers. With a substantially continuous coating, little or no surfacearea of the fibers is exposed and the desired characteristics added tothe fibers by the binder material are not nullified or significantlyaltered by uncoated areas of the fiber. With a binder level of at leastabout 10 percent of the combined dry weight of the binder material andfibers, and with the binder material being heat fusible, the coatedfibers are capable of bonding relatively strongly to one another whenheat fused. In addition, binder levels of 30 percent to 50 percent andhigher, such as above 90 percent and with no maximum limit yet beingdetermined, can be obtained using the process of the present invention,while still resulting in a product comprised of substantially unbondedindividualized fibers. At these higher levels of binder, the treatedfibers may readily be mixed or blended with untreated fibers and used inheat fusing the blended fibers. Also, higher binder levels arepreferably used to adhere solid super absorbent particulate materials tothe fibers.

Super absorbent particulate material is applied to the fibers while theliquid binder material on the fibers is still at least partially wet. Asthe liquid binder material dries, the super absorbent particulatematerial is adhered to the fibers.

As another aspect of the present invention, it has also been discoveredthat binders of the type with free carboxyl groups produce especiallystrong adhesion of the super absorbent particles and fibers.

In accordance with the method, more than one binder material may beapplied to the fibers, such as a thermoset binder material followed by athermoplastic binder material with the super absorbent particulatematerial being adhered to the fibers by the binder. Again, substantiallyindividualized fibers containing these plural binder materials can beproduced in accordance with the method. Individualized fibers refers tothe fibers being substantially unbonded to one another, although they doadhere to the super absorbent particles.

As another feature of the method of the invention, the fibers may beheated following the application of the liquid binder, and after theapplication of the super absorbent particulate material, to acceleratethe drying of the fibers.

Although not as beneficial for many applications, such as when theproperties of individual fibers are desired, in addition to individualfibers, fiber bundles may also be included in the fiber product. A fiberbundle is an interconnected group of two or more fibers that are notseparated during processing. Fiber bundles, like individual fibers aremuch longer than wide. For example, when mechanically fiberized wood isproduced, some individual fibers result along with fiber bundles offibers that are not separated during the mechanical fiberizationprocess.

It is accordingly one object of the present invention to providediscontinuous fibers coated with one or more binder materials and withthe fibers adhered to super absorbent particles by the binder.

It is another object of the present invention to provide such bindercoated fibers which are substantially individualized or unbonded otherthan to super absorbent particles.

A further object of the present invention is to provide a method ofcoating discontinuous fibers with liquid binders applied in an amountwhich is sufficient to substantially continuously coat the fibers or inmuch higher amounts, the liquid binder adhering the fibers to superabsorbent particles.

Another object of the present invention is to provide substantiallyindividualized discontinuous fibers coated with a heat fusible bindermaterial, with super absorbent particulate materials adhered thereto,and in which the binder may be subsequently heated to bond the fibers,with or without additional untreated fibers being added.

A further object of the invention is to form an air laid web directlywith dried coated fibers and with partially wet coated fibers.

A subsidiary object of the present invention is to also treat fiberbundles in the same manner as individual fibers are treated.

These and other objects, features and advantages of the presentinvention will be apparent with reference to the following detaileddescription and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of one form of apparatus in whichdiscontinuous fibers can be treated in accordance with the method of thepresent invention.

FIG. 2 is a side elevational section view of one form of binderapplication mechanism which can be used to apply liquid binder materialto discontinuous fibers in accordance with the method of the presentinvention.

FIG. 3 is a front elevational section view of the binder applicationmechanism of FIG. 2.

FIG. 4 is a schematic illustration of another form of binder applicationmechanism which can be used to product the fiber product of the presentinvention.

FIG. 5 is a schematic illustration of an alternative apparatus used inproducing the fiber product of the present invention.

FIG. 6 is a schematic illustration of an apparatus for producing thefiber product of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a fiber product comprised of treateddiscontinuous synthetic and natural fibers. The term discontinuousfibers refers to fibers of a relatively short length in comparison tocontinuous fibers treated during an extrusion process used to producesuch fibers. The term discontinuous fibers also includes fiber bundles.The term individual fibers refers to fibers that are comprisedsubstantially of individual separated fibers with at most only a smallamount of fiber bundles. Chopped or broken synthetic fibers also fallinto the category of discontinuous fibers. Although not limited to anyparticular type of fiber, the synthetic fibers commonly are ofpolyethylene, polypropylene, acrylic, polyester, rayon and nylon.Discontinuous fibers of inorganic and organic materials, includingcellulosic fibers are also included. The natural fibers may likewise beof a wide variety of materials, with chopped silk fibers, wood pulpfibers, bagrasse, hemp, jute, rice, wheat, bamboo, corn, sisal, cotton,flax, kenaf and the like, and mixtures thereof, being several examples.

Wood pulp fibers can be obtained from well-known chemical processes suchas the kraft and sulfite processes. Suitable starting materials forthese processes include hardwood and softwood species, such a alder,pine, douglas fir, spruce and hemlock. Wood pulp fibers can also beobtained from mechanical processes, such as ground wood, refinermechanical, thermomechanical, chemi-mechanical, andchemi-thermomechanical pulp processes. However, to the extent suchprocesses produce fiber bundles as opposed to individually separatedfibers or individual fibers, they are less preferred. However, treatingfiber bundles is within the scope of the present invention. Recycled orsecondary wood pulp fibers and bleached and unbleached wood pulp fiberscan also be used. Details of the production of wood pulp fibers arewell-known to those skilled in the art. These fibers are commerciallyavailable from a number of companies, including Weyerhaeuser Company,the assignee of the present patent application.

For purposes of convenience, and not to be construed as a limitation,the following description proceeds with reference to the treatment ofindividual chemical wood pulp fibers. The treatment of individual fibersof other types and obtained by other methods, as well as the treatmentof fiber bundles, can be accomplished in the same manner.

When relatively dry wood pulp fibers are being treated, that is fiberswith less than about 10 to 12 percent by weight moisture content, thelumen of such fibers is substantially collapsed. As a result, whenbinder materials, in particular latex binder materials, are applied tothese relatively dry wood pulp fibers, penetration of the binder intothe lumen is minimized. In comparison, relatively wet fibers tend tohave open lumen through which binder materials can flow into the fiberin the event the fiber is immersed in the binder. Any binder thatpenetrates the lumen contributes less to the desired characteristics ofthe treated fiber than the binder which is present on the surface of thefiber. Therefore, when relatively dry wood pulp fibers are treated, lessbinder material is required to obtain the same effect than in the casewhere the fibers are relatively wet and the binder penetrates the lumen.

Binders used to treat the fibers broadly include substances which can beapplied in liquid form to entrained fibers during the treatment process.These binder materials are preferably of the type which are capable ofsubsequently binding the fibers produced by the process to one anotheror to other fibers during the manufacture of webs and other productsusing the treated fibers. Most preferably these binders comprise organicpolymer materials which may be heat fused or heat cured at elevatedtemperatures to bond the fibers when the fibers are used inmanufacturing products. Also, the binder must be of a type which issuitable for the purpose of adhering the fibers to super absorbentparticles.

Suitable binders include polymeric materials in the form of aqueousemulsions or solutions and nonaqueous solutions. To preventagglomeration of fibers during the treatment process, preferably thetotal liquid content of the treated fibers during treatment, includingthe moisture contributed by the binder together with the liquid contentof the fibers (in the case of moisture containing fibers such as woodpulp), must be no more than about 45 to 55 percent of the total weight,with a 25 to 35 percent moisture content being more typical. Assumingwood pulp is used as the fiber, the moisture contributed by the woodpulp can be higher, but is preferably less than about 10 to 12 percentand more typically about six to eight percent. The remaining moisture orliquid is typically contributed by the binder. These polymer emulsionsare typically referred to as "latexes." In the present application, theterm "latex" refers very broadly to any aqueous emulsion of a polymericmaterial. The term solution means binders dissolved in water or othersolvents, such as acetone or toluene. Polymeric materials used inbinders in accordance with the present method can range from hard rigidtypes to those which are soft and rubbery. Moreover, these polymers maybe either thermoplastic or thermosetting in nature. In the case ofthermoplastic polymers, the polymers may be a material which remainspermanently thermoplastic. Alternatively, such polymers may be of a typewhich is partially or fully cross-linkable, with or without an externalcatalyst, into a thermosetting type polymer. As a few specific examples,suitable thermoplastic binders can be made of the following materials:

ethylene vinyl alcohol

polyvinyl acetate

acrylic

polyvinyl acetate acrylate

acrylates

polyvinyl dichloride

ethylene vinyl acetate

ethylene vinyl chloride

polyvinyl chloride

styrene

styrene acrylate

styrene/butadiene

styrene/acrylonitrile

butadiene/acrylonitrile

acrylonitrile/butadiene/styrene

ethylene acrylic acid

polyethylene

urethanes

polycarbonate

polyphenylene oxide

polypropylene

polyesters

polyimides

In addition, a few specific examples of thermoset binders include thosemade of the following materials:

epoxy

phenolic

bismaleimide

polyimide

melamine/formaldehyde

polyester

urethanes

urea

urea/formaldehyde

As explained more fully below, in accordance with the method of thepresent invention, more than one of these materials may be used to treatthe discontinuous fibers. For example, a first coating or sheath of athermoset material may be used followed by a second coating of athermoplastic material. The super absorbent particles are then typicallyadhered to the outer binder material. During subsequent use of thefibers to make products, the thermoplastic material may be heated to itssoftening or tack temperature without raising the thermoset material toits curing temperature. The remaining thermoset material permitssubsequent heating of the fibers to cure the thermoset material duringfurther processing. Alternatively, the thermoset material may be curedat the same time the thermoplastic material is heated by heating thefibers to the curing temperature of the thermoset with the thermoplasticmaterial also being heated to its tack temperature.

Certain types of binders enhance the fire resistance of the treatedfibers, and thereby of products made from these fibers. For example,poly vinyl chloride, poly vinyl dichloride, ethylene vinyl chloride andphenolic are fire retardant.

Surfactants may also be included in the liquid binder as desired. Othermaterials may also be mixed with the liquid binder to impart desiredcharacteristics to the treated fibers. For example, particulatematerial, such as pigments, may also be included in the binder forapplication to the fibers.

In addition, super absorbent particulate materials are adhered to thefibers to provide desired functional characteristics. The solidparticulate materials are applied to a binder wetted surface of thefibers and are then adhered to the fibers by the binder as the binderdries. In this case, heat curing or heat fusing of the binder is notrequired to adhere the particles to the fibers. Thus, the superabsorbent particles are not coated with the binder, which couldinterfere with their optimum liquid absorption. In addition to superabsorbent particulate materials, other particulate materials may also beadhered to the fibers. Examples of such other particulate materialsinclude pigments, such as titanium dioxide; fire retardant materials,such as alumina trihydrate and antimony oxide; electrically conductivematerials, such as metallic powders and carbon black; abrasivematerials, such as ceramics, grit and metallic powders; acidularmaterials, such as clay, talc and mica, used as papermaking additives;oleophilic materials; hydrophobic materials; and other hydrophilicmaterials; insecticides; and fertilizers. Thus, the solid particulatematerials are not limited to narrow categories.

The super absorbent particulate materials are granular or powderedmaterials which have the ability to absorb liquids, including bodyfluids. These super absorbents are generally hydrophilic polymericmaterials. Super absorbents are defined herein as materials whichexhibit the ability to absorb large quantities of liquids, i.e. inexcess of 10 to 15 parts of liquid per part thereof. These superabsorbent materials generally fall into three classes, namely, starchgraft copolymers, cross-linked carboxymethylcellulose derivatives andmodified hydrophilic polyacrylates. Without limiting the generality ofthe term super absorbent, examples of super absorbents includecarboxylated cellulose, hydrolyzed acrylonitrile-grafted starch, acrylicacid derivative polymers, polyacrylonitrile derivatives, polyacrylamidetype compounds and saponified vinyl acetate/methyl acrylate copolymers.Specific examples of super absorbent particles are marketed under thetrademarks SANWET super absorbent particles (supplied by Sanyo KaseiKogyo Kabushiki Kaisha) and SUMIKA GEL super absorbent particle(supplied by Sumitomo Kagaku Kabushiki Kaisha).

An abrasive is a hard substance that, in particulate form, is capable ofeffecting a physical change in a surface, ranging from the removal of athin film of tarnish to the cutting of heavy metal cross sections andcutting stone. Abrasives are used in scores of different abrasiveproducts. The two principal categories of abrasives are: (1) naturalabrasives, such as quartz, emery, corundum, garnet, tripoli,diatomaceous earth (diatomite), pumice, and diamond; and (2) syntheticabrasives, such as fused alumina, silicon carbide, boron nitride,metallic abrasives, and synthetic diamond.

Oleophilic materials are those capable of rapid wetting by oil whilehydrophilic materials are those capable of rapid wetting by water.

Pigments or colorants can broadly be defined as being capable ofreemitting light of certain wavelengths while absorbing light of otherwavelengths and which are used to impart color.

Electrically conductive materials are those which readily conductelectric current.

In addition, fire retardant materials are those which reduce theflammability of the fibers to which they are attached. Preferably thesematerials are active fire retardants in that they chemically inhibitoxidation or they emit water or other fire suppressing substances whenburned.

With reference to FIG. 1, a sheet of chemical wood pulp 10 is unrolledfrom a roll 12 and delivered to a refiberizing apparatus, such as aconventional hammer mill 14. The sheet 10 is readily converted intoindividual fibers 16 within the hammer mill. These individual fibers aredelivered, as by a conveyor 18, to a fiber loading zone 20 of a fibertreatment apparatus. In the case of a continuous process, fibers 16 arecontinuously delivered to the zone 20. In a batch or semi-batch process,fibers are loaded at zone 20 at intervals.

In the FIG. 1 fiber treatment apparatus, loading zone 20 forms part of afiber treatment conduit 24. The illustrated conduit 24 comprises arecirculating loop. A blower or fan 26 in the loop 24 is positionedadjacent to the fiber loading zone 20. Blower 26 is capable of moving agaseous medium, such as air, at a velocity and volume sufficient toentrain the fibers which have been loaded into zone 20. The entrainedfibers circulate in a direction indicated by arrow 28 through the loopand pass through the loading zone 20 and blower 26 each time the loop istraversed.

The velocity of air traveling in the loop is preferably set at a levelwhere solids are uniformly dispersed and transported by the air flow. Inaddition, the velocity is preferably established at a level which issufficient to avoid saltation, that is the dropping of solids or liquidsfrom a horizontal air stream. As a specific example, when Type NB316chemical wood pulp, available from Weyerhaeuser Company, was used as thefiber, a velocity of 5,000 feet per minute worked extremely well fortreatment of these fibers. However, this velocity can be varied andadjusted for optimum results.

Also, the ratio of the volume of air per pound of entrained fiber isvariable over relatively large ranges. One suitable example is 23.4 ft³of air per pound of fiber. As another example, 11.7 ft³ of air per poundof fiber produced equivalent results.

The entrained fibers traveling in the loop pass one or more bindermaterial application zones, with one such zone being indicated in FIG. 1at 30. This binder material application zone 30 forms a part of theconduit 24. A mechanism is provided at the binder application zone forapplying a liquid binder solution to the entrained fibers. In the FIG. 1form of this mechanism, plural nozzles, in this case nozzles 32, 34 and36, are used to apply the liquid binder material. These nozzles producean atomized spray or mist of binder drops which impact and coat thefibers as the fibers pass the nozzles.

In the FIG. 1 apparatus, plural valves 40, 42 and 44 are operated tocontrol the flow of liquid binder material to the respective nozzles 32,34 and 36. In the illustrated configuration, a first liquid bindermaterial from a tank or other source 46 is delivered to the threenozzles 32, 34 and 36 when valves 40 and 42 are open and valve 44 isclosed. As the fibers recirculate through the conduit 24, and each timethey pass the nozzles, an additional amount of the first liquid bindermaterial is applied. Different surfaces of the fibers are exposed to thenozzles 32, 34 and 36 as the fibers travel through the materialapplication zone 30. After the desired amount of the first liquid bindermaterial is applied, the valve 40 is closed. If desired for a particularapplication, a second liquid binder material from a tank or other source48 may also be applied to the fibers. With valves 42 and 44 open andvalve 40 closed, this second liquid binder material is applied to thefibers through each of the nozzles 32, 34 and 36. In addition, the twoliquid binder materials may be simultaneously applied, at successivelocations in zone 30. For example, the valve 42 may be closed and valve44 opened so that the first liquid binder material is applied throughnozzles 32, 34 and the second liquid binder material is applied throughnozzle 36. More than two types of liquid binder materials may be appliedby adding additional binder sources and suitable valving and nozzles.

In general, the material application zone 30 typically ranges from twoto one hundred feet long, with longer application zones allowing theapplication of binder over a longer period of time during passage offibers through the material application zone. Also, longer materialapplication zones facilitate the use of more nozzles spaced along thelength of the zones.

The nozzles 32, 34 and 36 are commercially available and produce a finemist of droplets. Typically, these nozzles provide a fan spray. Anysuitable nozzles may be used, but it is desirable that the nozzles notproduce a continuous stream of liquid binder material, but insteadproduce droplets or a mist of such material. The nozzles are typicallyspaced apart from three to four feet along the length of the conduit,although they may be closer or further apart as desired.

Virtually any amount of binder material may be applied to the entrainedfibers. However, it has been found that the application of binder mustbe at a minimum of about seven percent of the dry weight of the combinedfibers and binder in order for the fibers to have a substantiallycontinuous sheath or coating of the binder material. If the fibers lacka continuous coating, it becomes more difficult to adhere significantamounts of super absorbent particulate material to the binder in themanner explained below. In fact, a much higher percentage of binder thanthis minimum is preferably used to adhere these particles and thefibers. Also, exposed portions of the core fiber, that is surface areasof the fiber not coated with the binder, lack the desiredcharacteristics of the binder. For example, if a hydrophobic binder isused to cover a water absorbing cellulose material, failure tocompletely enclose the material with the coating leaves exposed surfacesof the fiber which can absorb water. Also, any uncoated areas on thefibers would not bond to other untreated fibers during subsequent heatbonding of the treated and untreated fibers.

It has also been found that, with a binder concentration of about 10percent by dry weight of the weight of the fiber and binder combination,the fibers, when heat fused, will bond somewhat strongly to other fiberscoated in a similar manner, but less strongly to untreated fibers. Theresulting bond strength is similar to the strength achieved when fiberscoated with a 40 percent by dry weight binder amount are mixed withuntreated fibers in a ratio of one part treated fiber to three partsuntreated fiber. A binder concentration by dry weight of the combinedbinder and fibers of from 30 percent to 50 percent has proven extremelysuitable for use in mixing with other fibers, heat bonding, and use informing products such as absorbent pads.

Binder concentrations in excess of 50 percent, for example 90 percent ormore, can be achieved utilizing the present invention. To achieve theseextremely high binder concentrations, one preferred approach is to applya first amount of the binder material to the entrained fibers, continueto recirculate the fibers until this first layer or coating of bindermaterial is substantially dry, and then apply a second coating of thebinder material. Third, fourth and subsequent coatings can be applied tothe entrained fibers as necessary to achieve the desired level of bindermaterial.

Following the application of the liquid binder material to the fibersand the super absorbent particulate material as explained below, thefibers may be retained in the loop until they have dried. Therecirculation of the fibers may then be stopped and the fibers removedat the loading zone 20, which then functions as a fiber removallocation. However, in the FIG. 1 apparatus, a cyclone separator 60 isselectively connected by a conduit section 61 and a gate valve 62 to theconduit 24. At the same time a valve 64 is opened to allow air to enterthe loop 24 to compensate for air exiting through the separator 60. Withthe separator in the loop, the entrained fibers are collected in theseparator and then removed from the separator at a fiber removal outlet66. A substantial majority of the fibers processed in this manner areunbonded to one another by the binder material. By substantial majority,it is meant that at least about 70 percent of the fibers remainunbonded. More specifically, in tests conducted as of this time, theresulting treated fibers are substantially unbonded, meaning thatapproximately 95 percent of the treated fibers have been found to beunbonded to one another by the binder material. However, plural fibersare bonded to the super absorbent particles.

An optional means for heating the binder coated fibers may be includedin conduit 24. For example heated air may be blended with the airflowing through the conduit. Similarly, a heater 70 may be included inconduit 24 for heating the fibers. This added heat accelerates thedrying of the liquid binder and adhered super absorbent particles. Inthe event a thermoplastic heat fusible binder is used, the fibers arepreferably heated above the film forming temperatures of the binder andbelow the hot tack temperature at which the binder becomes tacky so thatthe binder coated fibers may subsequently be heat fused duringprocessing of the fibers into products. Also, if a thermoset heatfusible binder is used, the fiber temperature is preferably maintainedbelow the curing temperature of the binder so that the binder coatedfibers may be subsequently heat cured during the processing of thebinder coated fibers into products.

The fibers are preferably not heated prior to the application of thebinder material. It has been found that heating the fibers results inelevated temperatures at the binder application zone 30. These elevatedtemperatures cause some of the binder to at least partially dry(coelesce) before reaching surfaces of fibers passing through the binderapplication zone 30. The solidified binder tends to either not adhere,or only adhere weakly, to the fibers. In addition, droplets of binderwhich impinge heated fibers tend to dry in globules on the fibers,rather than spread across the surface of the fibers to provide asubstantially continuous uniform coating thereon.

The dried fibers from outlet 66 of the cyclone separator 60 may bedeposited in a conventional baling apparatus 72 to prevent bonding ofthe fibers in the baler, the fibers are at a temperature which is belowtheir curing or tack temperature under the pressure applied by thebaler. When compressed, these fibers remain unbonded by the bindermaterial.

Also, treated fibers which have only been partially dried, and thuswhich are still somewhat wet with the binder material, may be depositedfrom outlet 66 loosely onto a conveyor 74 or in a loose uncompressedpile at a collecting zone (not shown). These fibers can then be allowedto dry. Alternatively, the treated fibers may be carried by the conveyor74 through a heater 76, operable like heater 70, to accelerate thedrying of the fibers. The resulting product again contains a majorportion of unbonded fibers. However, the wetter the fibers and moredense the resulting web when deposited on belt 74, or in a pile, themore binder-to-binder bonds that occur. Thus, in many cases it ispreferable to at least partially dry the fibers within the conduit 24prior to removing the fibers therefrom. However, the fiber may be airlaid either dry or wet, that is with no more than about a 55 percenttotal moisture content in the fibers and binder thereon, directly into aweb which can then be processed into various products, such as intodisposable diapers with the core of the diaper being formed by the web.Air laying refers to the transfer of the fibers through air or anothergaseous medium.

As previously mentioned, super absorbent particles, as well as othersolid particulate materials, may be adhered to the fibers by the bindermaterial. Due to the relatively large size of super absorbent particles,plural fibers are in effect adhered to the particles.

To accomplish this, the solid particulate material, such as superabsorbent particles, is added to the loop 24, such as at the fiberloading zone 20. The particles may also be added to the loop 24 from asupply housing 80, using a feed screw metering device or otherconventional injection mechanism. Preferably, the particles are addedafter the fibers have been wetted with the binder material.Consequently, the particles will not be covered with the bindermaterial, which could interfere with the desired attributes contributedby the particles. These particles contact the wet binder material on thesurfaces of the fibers and stick to the binder material. As the bindermaterial dries, the particles remain stuck to the surface of the treatedfibers. In one specific approach, the fibers are treated with a binder,circulation of the fibers is stopped momentarily to allow the additionof the solid particulate material at the fiber loading zone 20, andrecirculation and entrainment of the fibers is recommenced. Theparticles mix with and are secured to the surface of the fibers by theliquid binder material as the binder dries. Although lowerconcentrations are effective in binding particles to fibers, it has beenfound that relatively high levels of binder concentrations, for example20 percent or more of the dry weight of the binder, fiber and additive,produces the best adhesion of particles to the fibers. A 50 percentbinder concentration would perform better at adhering particles to thefibers than a 20 percent binder concentration in many applications.These higher binder levels, when heat fusible binders are used,facilitate subsequent heat fusion of the fibers and strong bonding, withor without other fibers being added, during use of the fibers inmanufacturing products.

The FIG. 1 apparatus may be operated in a batch mode in which fibers areintroduced, fully treated and removed. Alternatively, a semi-batchapproach may be used in which fibers are added and some, but not all, ofthe fibers removed from the loop. Also, the FIG. 1 apparatus may beoperated in a continuous mode in which fibers are introduced at zone 20and removed by the cyclone separator 60 with or without recirculatingthrough the loop. The gate valves 62, 64 may be opened to a desiredextent to control the amount of fiber that is removed. This quantity ofremoved fiber is preferably equal to the amount of untreated fiber thatis introduced into the loop. In this nonrecirculating case, the zone 30is typically expanded.

With reference to FIGS. 2 and 3, another mechanism for applying bindermaterial to the fibers is illustrated. Rather than using external spraynozzles such as 32, 34 and 36, plural nozzles (i.e., one being shown as82 in FIGS. 2 and 3) are included in the conduit at the binder materialapplying zone 30. The nozzle 82 applies a fine spray of liquid bindermaterial onto the fibers 16 as they move past the nozzle. The FIGS. 2and 3 binder applying mechanism includes a means for impartingturbulence to the air as it passes the nozzles. As a result, the fibers16 tend to tumble in front of the nozzles and expose different surfacesto the applied binder material. The illustrated turbulence impartingmechanism comprises a blunted conical air deflection baffle 86 supportedwithin the conduit 24 by rods, with two such rods 88 and 90 being shown.Rod 90 may be hollow to provide a pathway through which binder materialis delivered to the nozzle 82. Of course, other turbulence impartingmechanisms may also be used.

In FIG. 4, a rotary mixer 90 with plural mixing paddles, some beingindicated at 92, is disposed within the conduit 24 at the materialapplying zone 30. This mixer is rotated by a motor (not shown) to impartturbulence to fibers as they pass the mixer paddles. The nozzles 32, 34and 36 are disposed externally of the conduit 24 for directing thebinder material through ports to the fibers passing the mixer. Thesenozzles may be enclosed in a shroud or cover as shown by dashed lines 94in this figure. However, in the FIG. 4 approach, blower 26 has beenshifted to a location downstream from the material applying zone 30.Consequently, the material applying zone is at a relatively low pressurewith a slight vacuum being present in the material applying zonerelative to the pressure outside the conduit at this zone. Consequently,fibers passing the nozzles 32, 34 and 36 tend to be drawn into theconduit rather than escaping through the binder applying ports. As aresult, the nozzles can be positioned outside of the conduit where theyare not subject to being clogged by the passing fibers.

Referring to FIG. 5, another apparatus is shown for producing the fiberproduct of the present invention. In FIG. 5, for purposes ofconvenience, elements in common with those of FIG. 1 have been givenlike numbers and will not be discussed in detail.

In general, the FIG. 5 form of the apparatus allows the continuousprocessing of fibers with the fibers passing only once through thebinder material application zone 30. However, the zone 30 is typicallyof an extended length with more nozzles (i.e. six to twelve or more)than shown in FIG. 5. Following the application of the binder material,super absorbent and optionally other solid particulate material may beadded from source 80, such as by a blower (not shown) or a feed screw,to introduce the particles into the stream of entrained fibers. Thefibers pass through a heater or oven 70, or heated air is blended withthe air stream which entrains the fibers, for drying purposes and thentravel through a distance D at the elevated temperatures created by thisheat. As a typical example, D may be 150 feet with the time required totravel the distance D enabling the binder on the entrained fibers tobecome substantially dry. Optionally, cooling air from a refrigerationunit 100 or ambient air from the environment may be delivered by ablower 102 to the conduit 24 at a location 104 in the conduit. Thiscooling air lowers the temperature of the dried and treated fibers. Thecooling air may be dehumidified prior to introduction to conduit 24 tominimize any condensation that may otherwise occur in the conduit. Wherethermosetting binders are used, preferably the added heat does notelevate the temperature of the fibers to a level which cures thethermosetting binder. Consequently, the binders may subsequently be heatcured when the treated fibers are thereafter used in manufacturing.Also, where thermoplastic binders are used, the temperature ispreferably kept above the film forming temperature and below the hottack temperature of the thermoplastic binder material. Cyclone separator60 may be provided with a bleed line 106 for venting the air duringseparation. Although less preferred, this air may be recirculated backto the fiber loading zone 20. Flow control gate valves 107, 109 may beincluded in the system to balance the air flow through the variousconduits of the illustrated system.

The treated fibers from outlet 66 of the separator 60 may be fed to ahopper 110 of a conventional fiber blending unit 112. Other fibers, suchas wood pulp fibers or synthetic fibers are fed, in a desired proportionfor the resulting product, by way of a conduit 114 to another hopper 116and then to the blending unit 112. The fibers from outlet 66 can also beused without blending them with other fibers. The blended treated anduntreated fibers 118 are shown being deposited on a facing sheet 120which is passed through the blending unit 112 from a roll 122. Thefibers may also be deposited directly on a conveyor without a facingsheet. The facing sheet is carried by a conveyer 124 through theblending unit 112. The composite web is then passed through athermobonding unit 130 which raises the temperature of the fiberssufficiently to cause the treated fibers to heat fuse to the otherfibers and to the facing sheet. The fibers may be compressed to densifythe web prior to or after delivery to the thermobonder 130. A coversheet may also be added to the product before or after the thermobonder130. Following thermobonding, to reduce the stiffness of the webs, theymay be "tenderized" by the use of a mechanism which mechanically breaksup some of the bonds in the web. The web still remains substantiallybonded, however. As one example, the webs may be passed through the nipsof cross machine direction and machine direction corrugators to reducetheir stiffness. The stiffness can be controlled by adjusting theclearance between the nips. Although not limited to a specific approach,examples of suitable corrugators and tenderizing procedures aredisclosed in U.S. Pat. Nos. 4,559,050; 4,596,567 and 4,605,402. Theresulting material can be used in a conventional manner to manufacture awide variety of products, such as absorbent pads, disposable diapers,webs and the like.

In the FIG. 6 form of apparatus used to produce the fiber product of thepresent invention, the fibers to be treated may be delivered in looseform or in the form of a sheet 10 from roll 12 to a first hammer mill orrefiberizing device 140. The resulting fibers travel through air oranother gaseous medium in conduit 24 and through a binder applying zone30. If the fibers are not conveyed horizontally but merely passdownwardly in the conduit, the air velocity need not be as high. In thissense the fibers are not air entrained, but merely travel through theconduit. At zone 30, a first binder material 46 is applied to the fibersby way of nozzle 32. Again, this is a schematic representation of theapparatus, as plural nozzles are preferably employed and more than onetype of binder may be used. Thus, the material applying zone issubstantially elongated over that which is shown. Super absorbentparticulate material, with or without the optional particulatematerials, may also be added to the binder coated fibers from a sourceof such particles 80. The treated fibers may be air laid or otherwisedeposited, wet or dry directly on a face sheet 120 from a roll 122 ordirectly on a conveyor. Typically a vacuum (not shown) is used to drawthe fibers against the screen so that the fibers are not simply fallingunder the influence of gravity. The face sheet is carried by a conveyor124 past an outlet 146 of the fiber treatment apparatus. A web ofuntreated fibers 148 from a roll 150 is optionally delivered to anotherhammer mill 152 for fiberization and blending with the treated fibersprior to depositing the blend on the face sheet 120. The face sheet 120and deposited fibers may then be processed, such as previouslydescribed, for use in manufacturing a variety of products.

The following examples will serve to more specifically illustrate themethod of the present invention, although it is to be understood thatthe invention is not limited to these examples.

EXAMPLE 1

A bleached Kraft Southern Pine cellulose fiber pulp sheet (NB-316 fromWeyerhaeuser Company) was fiberized in a hammer mill. In addition, 1075grams of the fiberized fluff was then air entrained in a recirculatingconduit. After 20 seconds of air entrainment, sufficient PRIMACOR 4990ethylene acrylic acid copolymer solution (as a 20 percent solidsdispersion) was sprayed onto the air entrained fiber over a period ofeight minutes. PRIMACOR binder is a hydrophobic, somewhat oleophilicthermoplastic binder. Therefore, a PRIMACOR binder coated fiber iscapable of absorbing oil without water. PRIMACOR 4990 binder isavailable from Dow Chemical Corporation. In addition, a surfactantmaterial was added to the PRIMACOR binder for application with thebinder. In this specific example, Aerosol OT-S Dioctyl SodiumSulfosuccinate 70.2 percent TS, available from Cyanamid Corporation, wasused as the surfactant material. In this example, 1.74 percentsurfactant was included based on the PRIMACOR binder solids.

The loop was then opened and a desired amount of super absorbentparticles was deposited onto the damp fluff. A specific example of superabsorbent particles is SANWET 1M-1000 super absorbent particles,available from Celanese Corporation. The coated fiber was thenrecirculated for twenty seconds prior to removal from the loop.Recirculation of the materials through the loop mixed the particles withthe still wet and entrained fibers. Continued circulation of the libersresulted in partial drying of the binder and adhesion of the particlesto the fibers. The still somewhat wet coated fiber was then deposited ina loose pile and air dried at room temperature for 24 hours. Withpercentages expressed as the percent of the dry weight of the totalweight of the fiber, binder and super absorbent particle combination, anumber of samples were prepared in this manner, including:

1% PRIMACOR binder 20% super absorbent particles

2% PRIMACOR binder 40% super absorbent particles

2% PRIMACOR binder 50% super absorbent particles

5% PRIMACOR binder 50% super absorbent particles

10% PRIMACOR binder 50% super absorbent particles

15% PRIMACOR binder 20% super absorbent particles

20% PRIMACOR binder 50% super absorbent particles

With at least about a 7% binder concentration, a substantiallycontinuous binder coating of the fibers occurred. Even though woodfibers are of irregular cross-section and thus more difficult to coatthan surfaces with a regular cross section or smooth surface, theresultant fibers had a uniform continuous coating of binder. Also,approximately 95 percent of the fibers were unbonded to one another bythe binder material, although fibers were bonded to the super absorbentparticles. The dried fiber was then easily air laid in a laboratory padformer. Observations of the resulting pads confirmed that the binderadhered the fibers to the super absorbent particles, however very littleadhesion occurred at binder concentrations below about seven percent.More specifically, it has been found that a binder concentration of 7percent will adhere some particulate material to the fibers, but atbinder concentrations of 20 percent and higher of the total dry weightof the binder, fiber and additives, and higher, much better adhesionoccurs. Also, a very uniform distribution of super absorbent particleswas present in the resulting web and enhanced the water absorbingcharacteristics of the web.

It should be noted that the use of surfactants is desirable in manyapplications, but it not mandatory.

A wide variety of other binders have also been tested, includingSYNTHEMUL 40-800 and 40-850 emulsions, available from Reichhold ChemicalCorporation. Cellulose fibers having 5 percent, 7 percent, 10 percent,20 percent, 30 percent and 50 percent by dry weight SYNTHEMUL 40-800coating have been manufactured using the present method. Again, it isonly at levels of about 7 percent that a continuous coating of thefibers is achieved. At 5 percent, the binder material was present asnon-interconnected areas or blobs on the surface of the fibers. Thesepercentages are the percent of dry weight of the fiber and bindercombination which is the binder. In a recirculating system, to achievehigher percentages of the binder concentration, the fibers wererecirculated in the loop during liquid binder application for a longertime. SYNTHEMUL is a more hydrophilic binder than PRIMACOR binder. Also,ELVACE 40-712 binder, available from Reichhold Chemical Corporation, anethylene vinyl acetate, has also been tested as have a number of otherbinder materials. Super absorbent particles in the desired concentrationcan be adhered by the binding to these fibers. These tests have allconfirmed that fibers coated with a substantially continuous coating ofbinder material and adhered to super absorbent particles can be producedin accordance with the method of the present invention.

Preferably the binders are of a polymeric heat bondable type (forexample thermoset or thermoplastic binders) so that they may besubsequently heat bonded, with or without other fibers, in manufacturinga product. However, inorganic materials, such as liquid sodium silicate,in an amount sufficient to provide a substantially continuous coating ofthe fibers may also be used to adhere particles to the fibers. Althoughsuch materials are not used in binding fibers together during subsequentprocessing, they are capable of binding particles to the fibers and thusin this sense can be called binders. In addition, these materials, whencoated on the fibers, add characteristics to the fibers. For example,silicon dioxide increases the wetability of the fibers.

EXAMPLE 2

This example is similar to example 1 in that super absorbent particlesare adhered to the fibers by the binder material. Various amounts ofsuper absorbent particles have been successfully adhered to the fibers,including from 15-50 percent of the dry weight of the resultant fiber,binder and additive combination. Lower percentages are also possible asare higher percentages. Again, a specific example of super absorbentparticulate material is SANWET 1M-1000 super absorbent particles,available from Celanese Corporation.

In one more specific example of the method, rather than stopping thefibers to permit addition of the particulate material, super absorbentparticles were fed into the air stream containing the entrained fibersimmediately following the binder applicaton zone. The resultant materialhad fiber bonded to the super absorbent particles so as to contain thesuper absorbent particles in the resultant fluff. Yet, the fibers whichwere not attached to the particles were substantially unbonded to oneanother. The dried fluff was then air laid into a web and thermobonded.The web can also be air laid while the binder is wet if desired. The webwas tested for absorbency and found to be equivalent to an unbondedproduct, but with virtually 100 percent containment of the superabsorbent particles. In addition, the containment of the super absorbentparticles within the fibers prior to thermobonding was also excellent.Again, a very uniform distribution of super absorbent particles waspresent in the resulting web and enhanced the water absorbingcharacteristics of the web. Also, the placement of the super absorbentcontaining particles can be controlled by laying the fibers in aparticular portion of the web. With twenty percent and higherconcentrations, substantially all of the super absorbent particles wereretained in the fiber product. Consequently, the fibers can be storedand transported for subsequent use in products without significant lossor migration of super absorbent particles.

EXAMPLE 3

Thermoset materials may also be used in accordance with example 1 tocoat fibers to the desired percentage and to adhere super absorbentparticles to the coated fibers. For example, a mixture of polymericmethylene diisocyamate (PMDI) resin, such as PAPI 2027 resin from DowChemical Corporation and propylene carbonate from Arco ChemicalCorporation can be sprayed onto the fibers. Dioctyl sodiumsulfosuccinate may be used as a surfactant in this case. CASCOPHEN WC04resin from Borden Chemical Corporation is a specific example of asuitable phenolic resin. Still another example of a specific thermosetresin is CHEMBOND 2509 resin from Chembond, Inc. However, the inventionis not limited to specific thermoset binder materials.

Thus, fibers may be introduced into loading zone 20 and entrained. Asthe fibers travel past the material applying zone 30, nozzles apply thethermoset resin to the fibers. To increase the weight percentage ofthermoset resin, the fibers may be recirculated past the nozzles aplurality of times. Also, the lengths of the material zone and number ofnozzles may be extended to enhance the rate at which the fibers arecoated.

Resin in an amount of about 7 percent of the resin and fiber combinationhas ben found to be required to provide a continuous sheath or coatingof thermoset material. Very high weight percentages of thermoset resin,measured in the same manner, can be achieved with 90 percent and higherconcentrations expected.

EXAMPLE 4

In accordance with this example, functional materials in particulateform in addition to super absorbent particles can be adhered to thebinder coated fibers. These additional particulate materials may beadded in the desired percentage in the same manner as the superabsorbent particles. For example, these materials may be added to thesystem at the fiber loading zone 20 or introduced into the stream ofentrained binder coated fibers for adhesion by the wet binder to thefibers.

For example, fire retardant particulate materials, such as aluminatrihydrate and antimony oxide may be adhered to binder treated fibersfor use in preparing fire retardant materials, such as pads, paper andother products.

To produce an electrically conductive material, a conductive particulatematerial (such as 60-80 percent by weight of the binder fiber andadditive combination) may be adhered to the fibers by the binder.Powdered metallic materials and carbon black are examples.

For use in manufacturing abrasive pads and the like, abrasiveparticulate materials, such as ceramic powders, metallic powders, orgrit, may be secured to the fibers by the binder material.

Oleophilic materials, such as polynorbornene in a desired concentrationmay also be adhered to the fibers. NORSOREX particles from Norsorlor, adivision of CdF Chimie of Paris, France, is one example of such amaterial. Typically, a fugitive surfactant is used in this case. Likethe other particulate materials, these materials may be added in varyingpercentages.

In addition, more than one type of particle may be bound to the fibersif the functional characteristics of more than one particulate materialare desired.

EXAMPLE 5

In accordance with this example, the binder can be mixed with a blowingagent, such as Azodicarbonamid, and applied to the entrained fibers withthe super absorbent particles. When the fibers are subsequently heated,nitrogen, carbon dioxide and/or other gases would be released to producea foamed coating of the fibers. These foam coated fibers can then beused in manufacturing, such as in the manufacturing of low density waterabsorbing products.

EXAMPLE 6

In accordance with this example, the binder may be a hydrophobic resinor latex material with the particles hydrophilic and the binder may beof a hydrophilic material with the particles hydrophilic. A fugitivesurfactant is typically used when water based binders are used and thefibers or particles are hydrophobic.

An example of a hydrophobic binder with a hydrophilic particulatematerial would be fibers coated with PRIMACOR binder or with PMDI binderwith super absorbent particles adhered to the fibers by the binder. Forexample, fibers containing a 20 percent PRIMACOR binder, 40 percent byweight super absorbent particles, and 40 percent by weight fiber, havebeen produced. These percentages are of the total dry weight of thebinder, fiber and additive combination. Hexanol surfactants may be usedwith the binders as previously explained.

Finally, an example of a hydrophilic binder with hydrophilic particlesis SYNTHEMUL 40-800 binder as a binder and super absorbent particles asthe hydrophilic material.

EXAMPLE 7

The binder may also be comprised of a thermoplastic binder materialtogether with plasticizer particles which cause the polymer to softenwhen subjected to heat. A specific example of a liquid plasticizer isdioctyl phthalate. A specific example of a particulate plasticizer issold under the brand name SANTOWAX plasticizer from Monsanto, Inc.

EXAMPLE 8

In accordance with this example, the fibers may be coated with pluralbinder materials. For example, the first binder material may be athermoset binder material, such as phenolic resin, which can be appliedto the fibers to increase their strength and rigidity. CASCOPHEN WC04resin is an example of such a resin. This binder can be applied usingthe apparatus of FIGS. 1, 5 or 6. Following the application of the firstbinder, a second thermoplastic binder, such as PRIMACOR binder, can beapplied to the fibers. This second coating can then be used to bond thesuper absorbent materials to the fibers that would not bond as stronglyto a thermoset coating. During subsequent use of the fibers, they may beheated to the hot tack temperature of the outer binder coating forpurposes of heat fusing the fibers. However, because the thermosetcoating withstands higher temperatures, its integrity as a fiber andcontribution to the strength of the bicomponent fiber remains. Thus,fibers having plural desired characteristics, such as a water repellantundercoating and a highly bondable outer coating, can be produced, withthe adhered particulate super absorbent materials.

KRATON binder, a styrene butadiene block copolymer, available from ShellChemical Corporation is an example of another hydrophobic and oleophilicbinder material. This material does not form very strong bonds withother fibers. Therefore, a highly bondable first coating, such as ofPRIMACOR binder may be applied to continuously coat the fibers. KRATONbinder in a lesser amount may then be applied to only partially coat thefibers. Super absorbent particles may be also adhered to the binder. Theexposed PRIMACOR binder coated areas then enhance the bondability ofthese fibers.

EXAMPLE 9

This example illustrates the applicability of the process to cellulosefibers and fiber bundle material. Specifically, 1111 grams of amechanically fiberized wood (10 percent moisture) can be placed in arecirculating conduit 24 with an in-line blower. The blower can beturned on to entrain the wood fibers. 952 grams of Reichhold's SYNTHEMUL40-800 resin (55 percent moisture) can be sprayed onto the fiber througha port in the conduit. After addition of the latex, the super absorbentparticles in a desired amount can be added to the still wet fibers andair entrainment recommenced. The treated fiber material can then beshunted out of the loop 24, collected in a cyclone 60 and spread on abench to air dry.

EXAMPLE 10

It has been found that better adhesion of superabsorbent particles tofiber is achieved if the binder is of a type which has free carboxylgroups. In addition, the higher the percentage of free carboxyl groupsin the binder, the greater the observed strength of adhesion of thesuper absorbent particles to the fibers. Fibers with adhered superabsorbent particles were manufactured as explained above in connectionwith example 1. A comparison of the strengths of adhesion of superabsorbent particles was made with PRIMACOR binder as a binder and withSYNTHEMUL 40-504 resin, from Reichhold Chemical Corporation, as abinder. Equivalent amounts of these two binders were used. PRIMACORresin has a 20 percent carboxylation while SYNTHEMUL 40-504 resin has to1 to 3 percent carboxylation. In each case the super absorbent particleswere adhered to the fibers. However, when these treated fibers werepassed through a hammermill, fewer super absorbent particles separatedfrom the fibers treated with the higher carboxyl group containing binderthan separated from the fibers treated with the lower carboxyl groupcontaining binder. The carboxyl groups are believed to allow forhydrogen bonding between the particles and the binder.

Having illustrated and described the principles of our invention withreference to several preferred embodiments and examples, it should beapparent to those of ordinary skill in the art that such embodiments ofour invention may be modified in detail without departing from suchprinciples. We claim as our invention all such modifications as comewithin the true spirit and scope of the following claims.

We claim:
 1. A fiber product which comprises discontinuous fibers coatedat least partially with a thermoset binder material and which have solidparticles of super absorbent material adhered to the fibers by thethermoset binder material without the binder covering the particles, asubstantial majority of the fibers being substantially unbondedtogether.
 2. A fiber product comprised of fibers according to claim 1wherein the thermoset binder material is included in an amount which isat least seven percent by weight of the combined weight of thediscontinuous fibers and binder material, and wherein the thermosetbinder material substantially continuously coats the fibers.
 3. A fiberproduct according to claim 2 formed in a web, the binder having a heatcuring temperature, the binder being heated to a temperature above theheat curing temperature to heat bond the coated fibers to form the web.4. A compressed fiber product according to claim
 3. 5. A fiber productcomprised of fibers according to claim 1 formed in a web, the binderhaving a heat curing temperature, the binder being heated to atemperature above the heat curing temperature to heat bond the coatedfiber.
 6. A compressed fiber product according to claim
 5. 7. Acellulose product comprising cellulose fibers coated at least partiallywith a liquid heat fusible binder coating having a hot tack or heatcuring temperature, particles of a super absorbent material adhered tothe fibers by at least partially drying the heat fusible binder at atemperature below the heat tack or heat curing temperature without thesuper absorbent particles being covered by the binder, the heat fusiblebinder having been thereafter heated to a temperature above the tack orheat curing temperature to heat bond the coated fibers into a web.
 8. Acellulose product according to claim 7 formed in a web, the productincluding cellulose fibers without the coating which are heat bonded tothe coated fibers by the coating to form the web.
 9. A cellulose productaccording to claim 7 in which there are plural heat fusible binders. 10.A compressed cellulose product according to claim
 7. 11. A celluloseproduct according to claim 7 which is compressed before the binder isheated to a temperature above the tack or heat curing temperature.
 12. Acellulose product according to claim 7 which is compressed after thebinder is heated to a temperature above the tack or heat curingtemperature.
 13. A cellulose product according to claim 7 in which thebinder is included in an amount which is at least seven percent byweight of the combined weight of the cellulose fibers and the binder.14. A compressed cellulose product according to claim
 13. 15. Acellulose product according to claim 13 in which the bindersubstantially continuously coats the fibers.
 16. A cellulose productaccording to claim 15 formed in a web, the product including cellulosefibers without the coating which are heat bonded to the coated fibers bythe coating to form the web.
 17. A compressed cellulose productaccording to claim
 16. 18. A cellulose product according to claim 7 inwhich the binder comprises a thermoplastic binder.
 19. A celluloseproduct according to claim 7 in which the binder comprises a thermosetbinder.